fix a timing race flakiness in the added koa test

The ESM test case runs use-koa.mjs and expects some spans. It relies
on the ordering of those spans (based on start time). In some runs
two spans were starting in the same millisecond and the sort order
was ill-defined, which caused tests to fail.

plugins/node/opentelemetry-instrumentation-koa/test/fixtures/use-koa.mjs

@@ -17,6 +17,7 @@
 // Use koa from an ES module:
 //    node --experimental-loader=@opentelemetry/instrumentation/hook.mjs use-koa.mjs
 
+import { promisify } from 'util';
 import { createTestNodeSdk } from '@opentelemetry/contrib-test-utils';
 
 import { HttpInstrumentation } from '@opentelemetry/instrumentation-http';
@@ -38,6 +39,11 @@ import * as http from 'http';
 const app = new Koa();
 
 app.use(async function simpleMiddleware(ctx, next) {
+  // Wait a short delay to ensure this "middleware - ..." span clearly starts
+  // before the "router - ..." span. The test rely on a start-time-based sort
+  // of the produced spans. If they start in the same millisecond, then tests
+  // can be flaky.
+  await promisify(setTimeout)(10);
   await next();
 });
 

plugins/node/opentelemetry-instrumentation-koa/test/koa.test.ts

@@ -728,7 +728,7 @@ describe('Koa Instrumentation', () => {
         // a `simpleMiddleware`, then makes a single 'GET /post/0' request. We
         // expect to see spans like this:
         //    span 'GET /post/:id'
-        //    `- span 'middleware - simpleResponse'
+        //    `- span 'middleware - simpleMiddleware'
         //       `- span 'router - /post/:id'
         const spans = collector.sortedSpans;
         assert.strictEqual(spans[0].name, 'GET /post/:id');